FIG. 1 shows an example of an electromechanical actuator 100 of a valve 110 which comprises mechanical means, such as springs 102 and 104, and electromagnetic means with two electromagnets 106 and 108 for controlling the position of the valve 110 by means of electric signals.
In the example, the rod 113 of the valve 110 is applied for this purpose against the rod 112 of a magnetic plate 114 located between the two electromagnets 106 and 108.
When a current flows in the coil 109 of the electromagnet 108, the latter is activated and generates a magnetic field attracting the plate 114, which comes into contact with it.
This results in a displacement of the rod 112, which moves away from the rod 113, enabling the spring 102 to act to bring the valve 110 into the closed position, the head of the valve 110 coming against its seat 111 and preventing the exchange of gas between the interior and the exterior of the cylinder 116.
Analogously, when the electromagnet 108 is deactivated, when a current flows in the coil 107 of the electromagnet 106, the latter attracts the plate 114, which comes into contact with it and pushes the rod 112 by means of the spring 104 against the rod 113 such that the rod 112 acts on the valve 110 and brings the latter into the open position, the head of the valve being moved away from its seat 111 to permit, for example, the admission or the injection of gas into the cylinder 116.
Thus, the valve 110 alternates between the open or closed positions, called switched positions, with transient displacements between these two positions. The state of an open or closed valve will hereinafter be called the “switched state.”
The actuator 100 requires the use of a magnetic plate 114 of a heavy mass due especially to its considerable thickness Sp. This thickness is generally equal to the width Se of the branches of the electromagnets to achieve optimal functioning of the actuator. In fact, the branches of the electromagnet and the plate thus form a magnetic circuit of constant cross section.
However, the use of a plate 114 of a considerable cross section and consequently of a heavy mass has drawbacks. During the switching of the valve, in particular, the impact of the magnetic plate against the body of the electromagnet causes a considerable energy loss in the form of noise, especially because of the considerable velocities of the magnetic plate during the impact.
As this energy is proportional to the second power of the velocity of the plate, it is essential to reduce the velocity of this plate at the moment of impact.
However, as the electromagnetic force increases sharply when the plate is approaching the electromagnet, which causes a great acceleration, it is not easy to reduce the velocity at the moment of impact.
It is known that the velocity can be reduced by regulating the current flowing in the electromagnet to control the magnetic field of this electromagnet.
However, it is not easy to embody such a regulator because the electromagnetic force of the electromagnet, which force is applied to the magnetic plate during the approach of the electromagnet, varies nonlinearly with the air gap.
This nonlinearity is illustrated in FIG. 2, which is a diagram showing the changes in the electromagnetic force (on the ordinate) as a function of the value of the air gap (on the abscissa).
The present invention remedies the above-mentioned drawback.